What is the relationship between volume of a gas and its absolute temperature? Why does the temperature need to be converted from Celsius to Kelvin?
It's related to Charles's law.

Charles’ law is a relationship of temperature and volume. This law explains that as the temperature is increased, expansion of the gas will be seen. This is because as the temperature is increased; the kinetic energy increases as well, thus making the gases to expand.

`V = k T`

V is directly proportional to T. When volume (V) increases, it's because temperature (T) is increasing. The Expression for Charles law can be explained as:

`(V_1)/(T_1) = (V_2)/(T_2)`

Temperature should always be converted to kelvin for certain reasons. Kinetic theory of gases suggests that all movements of molecules will stop at 0 K (-273 C) or the absolute zero since the rate of movement of gases is a function of temperature. Celsius measuring was measured relative to water and was generally used around the world but has nothing to do with any of the gases.

according to charle's law, T(temperature) is propotional to V(volume).as the temperature increases the volume of gas also increases and vice-versa at constant pressure.

according to his experimental results as the temperature goes on decreasing at a point of temperature all the gas molecules get converted and in the container no gas molecules are present for all the gases. charle's defined this temperature as absolute temperature.V/T = CONSTANT (at constant Pressure)log V-log T= constantat zero kelvin or -273.15^o C volume of all gases become equal to zero.so it is called the absolute zero temperature or zero kelvin temperature or zero thermodynamic scale of temperature.For each degree change of temperature,the volume of the gas is changed by the fraction of 1/273 of its volume at 0^o C.

let the volume of the gas be Vo at 0^o C as the temperature increasesby t^o C,the new volume of gas becomes Vt,thus

Vt = Vo+Vo/273*t

Vt=Vo(1 +t/273)

Vt=Vo(273+t/273)

Vt/Vo=273+t/273

In kelvin scale there is no temperature readings in -ve values.so,it is accepted as the standard temperature scale.but the change in temperature remains constant in both kelvin and celsius scales.so it is necessary to convert ^o C into kelvin scale.